LONDON — Thousands of small intense earthquakes are rocking Iceland amid concerns that one of the country's volcanoes may be close to erupting.

Iceland has raised its aviation alert level for the risk of a possible volcanic eruption to orange — the second-most severe level. The alert is worrisome because of the chaos that followed the April 2010 eruption of Eyjafjallajokul, when more than 100,000 flights were cancelled because volcanic ash floating in the atmosphere is considered an aviation safety hazard.

Some 3,000 earthquakes have taken place since Saturday in Bardarbunga — a subglacial stratovolcano located under Iceland's largest glacier. Iceland's Meteorological Office said that no earthquakes above magnitude 3 have been recorded in the last 24 hours.

Seismologists said Tuesday magma is moving, but it is traveling horizontally.